The present disclosure relates to a phospholuminescent composition including a phosphor and also to a light source device including this phospholuminescent composition and a blue light source.
A phosphor having the composition of SrxBa2-xSiO4:Eu is one that is able to emit light in a bluish green to yellow region by excitation with light of a blue to near-ultraviolet region and has recently been considered for application to white LED (light emitting diode).
With this phosphor, it has been pointed out that an efficiency of excitation with light in a blue region is considerably lower than an efficiency of excitation with light in a near-ultraviolet region. It has been confirmed from excitation spectra that an excitation intensity in the blue region is significantly lower than an excitation intensity in the near-ultraviolet region (see, for example, Japanese Patent Laid-Open No. 2005-277441 and Applied Physics Letters Vol. 82, No. 5, 683 (2003)).
In general, because a desired emission wavelength band is obtained from a wide range depending on the selection of compositional ratio, the use of phosphors has been studied in, for example, thin displays called FPD (flat panel display) such as organic EL (electroluminescence) displays, plasma displays and the like.
These displays ordinarily have a light source device such as a backlight. In recent years, attention has been paid to phosphors capable of emitting light in a desired wavelength band and a light source device having an arrangement including a blue light source, such as LED, serving also as an excitation light source for phosphor. This is for the reason that such an arrangement brings about, in the light source device, many advantages in that a drive circuit can be made simpler in arrangement than with the case where all colors are obtained by direct drive light sources such as LED's and that peripheral members (resins, LED chips and the like) can be more suppressed from degrading than with the case where light in the near-ultraviolet region is used as an excitation light source.
Accordingly, phosphors serving to constitute such a light source device are strongly demanded in respect of an improvement in efficiency of excitation with such light in the blue region as mentioned above.